systat -vm: Humanize output for ease of reading.

Using 8 width is too wide for large numbers like 1379991K;
1330M is easier to read.

Submitted by: ota_j.email.ne.jp
Reviewed by: mckusick
MFC after: 2 weeks
Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D33495